In recent years, as demands for a high density and a high integration increase in the fields of semiconductors, optical/magnetic recordings, and the like, a micropatterning technology capable of patterning a size of several tens to several hundreds nanometers or smaller becomes indispensable. In this regard, a lot of researches have been made for elemental techniques in each process such as masks/steppers, exposure, and resist materials in order to implement such a micropatterning.
Although many studies have been made for resist materials, the resist material most widely used at this time is a photo-reactive organic resist (hereinafter, also referred to as a “photoresist”) that reacts to an exposure light source such as infrared light, an electron ray, and an X-ray (e.g., refer to Patent Literature 1 and Non-Patent Literature 1).
In the laser light used in exposure, the laser light intensity typically adjusted using a lens has a Gaussian distribution as illustrated in FIG. 1, where a spot diameter is defined as 1/e2. In general, reaction of the photoresist is initiated when energy expressed as E=hν (where E denotes energy, h denotes a Frank's constant, and ν denotes a wavelength) is absorbed. Therefore, since the reaction does not strongly depend on the light intensity, but depends on the wavelength of light, almost the entire portion where light is irradiated generates reaction (light irradiation portion≈exposure portion). For this reason, when the photoresist is used, reliable exposure would be achieved for the spot diameter.
The technique of using the photoreactive organic resist is very effective to forma fine pattern having a size of several hundreds nanometers. However, it is necessary to perform exposure with a spot diameter smaller than that of the pattern required in principle in order to use the photoreactive photoresist and form the fine pattern. Therefore, it is necessary to use KrF laser or ArF laser having a short wavelength as the exposure light source. However, such a light source unit is large-sized and expensive, and thus, it is not suitable in terms of reduction of the manufacturing cost. In addition, when an exposure light source such as an electron ray or an X-ray is used, it is necessary to provide an exposure atmosphere in a vacuum state. Therefore, a vacuum chamber is employed. This gives a considerable limitation in terms of the cost or the large size.
Meanwhile, if laser light having an intensity distribution illustrated in FIG. 1 is irradiated onto an object, a temperature of the object also exhibits a Gaussian distribution similar to the intensity distribution of the laser light. In this case, if a resist that reacts at a certain temperature or higher, i.e., a thermal-reactive resist is used, the reaction is processed in only the portion heated up to a predetermined temperature or higher as illustrated in FIG. 2. Therefore, it is possible to exposure a range smaller than the spot diameter (light irradiation portion≠exposure portion). That is, it is possible to form a fine pattern having a size smaller than the spot diameter without shortening the wavelength of the exposure light source. Therefore, it is possible to alleviate influence of the wavelength of the exposure light source by using the thermal-reactive resist.
Until now, techniques have been reported for forming a fine pattern through exposure or thermal/optical reaction caused by semiconductor laser and the like by using WOx, MoOx, noble metal oxides, and the like as a thermal-reactive resist (e.g., refer to Patent Literatures 2 to 4 and Non-Patent Literature 2). WOx and MoOx are known as a resist material called imperfect oxide having a degree of oxidation X smaller than that of perfect oxide. The degree of oxidation X is changed by heating through exposure, and a difference of solubility for the etchant is generated due to a difference of the degree of oxidation, so that a fine pattern can be formed through etching. For this reason, the etching characteristic is changed by a slight difference of the degree of oxidation X, so that a very high technique is necessary to manufacture a resist having excellent reproducibility based on a lot of parameters such as a condition of the start material, a method of forming a film, and an exposure method. In addition, tungsten (W) or molibdenum (Mo) problematically has a low resistance to a dry etching using a fluorine-based gas.
Meanwhile, noble metal oxide may be used to form the fine pattern by generating decomposition of noble metal oxide through thermal reaction, optical reaction, and the like and performing etching based on a difference of solubility for the etchant generated between decomposed and undecomposed portions. This technique is characterized in that a resist having excellent reproducibility can be obtained without significantly being influenced from a condition of the start material (for example, a slight difference of the degree of oxidation) because the material is decomposed at a certain temperature (decomposition temperature) in the case of, for example, thermal reaction. However, although the noble metal oxide used as the decomposed material in Patent Literatures 3 and 4 allows for pattern formation by generating decomposition reaction such as thermal reaction, optical reaction, and the like, a material particle growth is also generated along with the decomposition. Therefore, this technique takes only a sea-island structure in which a resist portion remaining after the etching is at random, and it is difficult to control a pattern size in a uniform convex-concavo or line-shaped fine pattern and the like.
The copper oxide as noble metal oxide generates abrupt decomposition to discharge oxygen when it reaches a decomposition temperature, and its particle growth is suppressed in comparison with the noble metal oxide used in Patent Literatures 3 and 4. Therefore, the copper oxide is an effective resist material for forming a fine pattern. However, although there are a number of etchants for copper as disclosed in Patent Literatures 5 to 8, there has not been reported for the selective etching of exposure/non-exposure portions with high precision when exposure is performed using noble metal oxide, particularly, copper oxide.